Rare species, Restionaceae, and the Cape flora

Abstract

AimI test whether species range size variation is driven by the age of the species, their intrinsic traits, environment or by historical‐geographical patterns (e.g. the location of climatic or environmental refugia).LocationGreater Cape Floristic Region (GCFR) of South Africa.TaxonAngiosperms, Restionaceae (restios).MethodsI determined the area of occupancy and extent of occurrence of all restios in the GCFR, and derive a list of “single‐site endemics” (SSE). I inferred a rate‐corrected and dated phylogeny which includes 98% of the species. I explored the correlates of range size variation with phylogenetically corrected regressions, focussing on likely candidate traits (dispersal and fire survival modes), habitats (soil drainage, elevation), climatic variables (rainfall and temperature) and history (age of species). I calculated the species richness, community mean range sizes and numbers of SSE for 49 sites and 938 10 m diameter circular relevés across the GCFR, and sought correlates of these, specifically testing for historical‐geographical patterns in relationship to the distance from the centre of the region.ResultsNarrow‐range restios are correlated with higher elevations, rainfall and rainfall seasonality; are found more likely in marshes and seepages; and are more likely killed by fire and have to re‐establish from seed after fire. Wide‐ranging species are found in areas with lower rainfall, at lower elevations, in well‐drained habitats, and resprout after fire. Community mean ranges sizes are larger towards the eastern part of the GCFR; and relevé data show that sandstones, shale, laterite and granites are associated with wider distribution ranges, as are soils with pebbles or sandy soils without rocks, and limestones with smaller community mean ranges than other bedrock types. The number of SSE is largely correlated with species richness, except that SSE are more likely at higher elevations.Main ConclusionRange size variation in the restios is largely driven by history (expressed as the distance from the Kogelberg region), suggesting that the Kogelberg region may have been most climatically stable during the Neogene and Pleistocene. The second‐most important driver is the environment (i.e. rock type, elevation, rainfall), generally with spatially restricted habitats hosting range‐restricted species.

Most lichens are rare, and degree of rarity is mediated by lichen traits and biotic partners

“…Although outside the scope of this investigation, we expect that numerous other environmental elements, especially those pertaining to features of a taxon's habitat and occupied ecoregion, also impact patterns of species richness and rarity in North American lichens (e.g. Angert et al, 2011; Goulson et al, 2005; Linder, 2019; Moreuta‐Holme et al, 2013; Sheth et al, 2020; Stevens, 1989; Taylor et al, 2019; Whitton et al, 2012). For example, in a landmark review of patterns of richness across taxonomic groups in North America, showed that bird species richness is highest along coastal regions and in the desert sky islands, mammal richness peaks in the southern and central Rockies and Sierras, and freshwater fish and amphibian richness are highest in the southeastern United States.…”

“…Similarly, the study of datasets built on finer‐scale geographical information may help to more clearly articulate nuances in the data, such as how distributions are impacted by topography, history, elevation, seasonality, specialization, phylogenetic relatedness, niche availability and/or disturbance (e.g. Goulson et al, 2005; Grünig et al, 2017; Harcourt, 2006; Linder, 2019; Sheth et al, 2020; Tripp et al, 2019; Whitton et al, 2012). Additionally, subsequent efforts to understand rarity among North American lichens would benefit from the generation of datasets with finer‐scale geographical information and more precise definitions of range sizes and datasets that take abundance into consideration.…”

“…For example, larger range sizes may lead to increased speciation rates as a function of increased opportunities to encounter novel habitats and isolating barriers (Gaston, 2003; Rosenweig, 1995). Indeed, there is evidence for a positive relationship between range size and lineage richness, and a negative relationship between lineage richness and rarity (Linder, 2019). However, a generalized relationship among life‐history traits, range size and species richness has yet to be established, and determinants of rarity remain further contested across axes of space, time and evolutionary relatedness (Angert et al, 2011; Brown et al, 1996; Grünig et al, 2017; Kreft & Jetz, 2007; Kunin, 1998; Lester et al, 2007; Linder, 2019; Rahbek, 2005; Sheth et al, 2020).…”

“…Indeed, there is evidence for a positive relationship between range size and lineage richness, and a negative relationship between lineage richness and rarity (Linder, 2019). However, a generalized relationship among life‐history traits, range size and species richness has yet to be established, and determinants of rarity remain further contested across axes of space, time and evolutionary relatedness (Angert et al, 2011; Brown et al, 1996; Grünig et al, 2017; Kreft & Jetz, 2007; Kunin, 1998; Lester et al, 2007; Linder, 2019; Rahbek, 2005; Sheth et al, 2020). Most prior research has targeted macroscopic plants and animals in understanding rarity (Brown et al, 1995; Harcourt, 2006; Kreft & Jetz, 2007; Moreuta‐Holme et al, 2013; Trakimas et al, 2016).…”

Disentangling the drivers of local species richness using probabilistic species pools

“…Species distribution models could be constructed for only 130 of the 350 restio species, for which enough location points were available. Many of these species for which SDMs could not be constructed are particularly range restricted, some 40 species are known only from single populations, and most are found in the western part of the Cape (Linder, 2019). Consequently, this could lead to an underestimation of the LPSPs in the western part of the Cape, relative to the eastern part.…”